System and method to manage transients for rapid power demand changes

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 62/004,534 filed May 29, 2014, the contents of which are hereby incorporated in their entirety.

FIELD OF TECHNOLOGY

The present disclosure generally relates to a system and a method for managing engine transients for rapid power demand changes, such as during engine loading and unloading.

BACKGROUND

Gas turbine engines may be used to supply power in various types of vehicles and systems, including, but not limited to, aircraft, naval propulsion, and the like. A gas turbine engine generally includes a compressor section, a combustor section, and a turbine section. The compressor section receives and compresses a flow of intake air. The compressed air then enters the combustor section in which a steady stream of fuel is injected, mixed with the compressed air, and ignited, resulting in high energy combustion gas, which is then directed to the turbine section. In the turbine section, the combustion gas causes turbine blades to rotate and generate energy, from which electrical power may be extracted via an electrical generator coupled mechanically or hydraulically to the gas turbine engine. The electrical power may be used by various loads within the vehicle or system, such as control systems, actuators, climate control systems, and the like.

In some situations, an electrical, hydraulic, or mechanical load may suddenly be removed, thereby reducing engine power demand, such that the gas turbine engine may be generating excess engine power. This in turn may result in rapid and undesirable acceleration of the gas turbine engine. In other situations, it may be desirable to go from a low power setting to one of instant high power, thereby increasing engine power demand. However, the gas turbine engine may require several seconds to achieve this state. At or near idle speeds, the gas turbine engine may be near the compressor surge line, and as such may need to be managed accordingly. This in turn affects the ability for the gas turbine engine to have a quick response.

Therefore, there exists a need for a system and method to manage engine transients when there is a rapid change in engine power demand, such as during engine loading and unloading, in an efficient and cost-effective manner.

BRIEF DESCRIPTION OF THE DRAWINGS

While the claims are not limited to a specific illustration, an appreciation of the various aspects is best gained through a discussion of various examples thereof. Referring now to the drawings, exemplary illustrations are shown in detail. Although the drawings represent the illustrations, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an example. Further, the exemplary illustrations described herein are not intended to be exhaustive or otherwise limiting or restricted to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary illustrations are described in detail by referring to the drawings as follows:

<figref idref="DRAWINGS">FIG. 1</figref> illustrates a schematic block diagram of an exemplary system for managing engine transients;

<figref idref="DRAWINGS">FIG. 2</figref> illustrates an exemplary gas turbine engine of the system of <figref idref="DRAWINGS">FIG. 1</figref>; and

<figref idref="DRAWINGS">FIGS. 3A and 3B</figref> illustrate an exemplary method for managing engine transients.

DETAILED DESCRIPTION

Gas turbine engines used in vehicles, such as aircraft, may experience transient loading and unloading conditions that may need to be managed. An exemplary system for managing engine transients may include a gas turbine engine having at least one compressor section configured to receive an inlet air stream, and at least one turbine section mounted on at least one spool. The gas turbine engine may be configured to operate at an engine power level to satisfy an engine power demand. The exemplary system may also include at least one generator operatively coupled to the gas turbine engine. The at least one generator may be configured to generate electrical power based at least in part on the engine power demand. The system further may include at least one heating element in communication with the at least one generator, and at least one control unit coupled to the at least one heating element. The at least one heating element may be configured to receive electrical power from the at least one generator to generate thermal energy. The at least one control unit may be configured to energize the at least one heating element if a first condition and/or a second condition exists. The first condition may include the engine power demand dropping below the engine power level, and the second condition may include an anticipated increase in the engine power demand. The at least one heating element may be located upstream of the at least one compressor section, such as in an inlet duct of the gas turbine engine, such that the thermal energy may be transferred to the inlet air stream.

An exemplary method of managing the engine transients may include first commanding the gas turbine engine and the generator to operate at an optimum speed for a current power setpoint. The method then may include determining if the first condition and/or the second condition exists. If so, the method then may include energizing the at least one heating element to convert at least a portion of the electrical power into thermal energy to exchange heat with an inlet air stream into the gas turbine engine.

Referring now to the figures, an exemplary system <b>100</b> for a vehicle or system, such as an aircraft, is shown in <figref idref="DRAWINGS">FIG. 1</figref>. The system <b>100</b> may include a gas turbine engine <b>101</b>, as depicted in <figref idref="DRAWINGS">FIG. 2</figref>. While the gas turbine engine <b>101</b> is depicted in <figref idref="DRAWINGS">FIG. 2</figref> as a turbofan, it should be appreciated that it may be, but is not limited to, a turbofan, a turboshaft, or a turboprop. The gas turbine engine <b>101</b> generally may include a compressor section <b>102</b> and a turbine section <b>104</b> mounted on a common shaft or spool. As seen in <figref idref="DRAWINGS">FIG. 2</figref>, the gas turbine engine <b>101</b> may be a multi-spool engine having low pressure (LP) and high pressure (HP) compressors and/or turbines. However, it should be appreciated that the gas turbine engine <b>101</b> may be a single spool engine. The compressor section <b>102</b> generally may be configured to receive and compress an inlet air stream <b>120</b>. The compressed air may then be mixed with a steady stream of fuel and ignited in a combustor section <b>103</b>. The resulting combustion gas may then enter the turbine section <b>104</b> in which the combustion gas causes turbine blades to rotate and generate energy.

The system <b>100</b> may also include a generator <b>106</b> coupled to the spool of the gas turbine engine <b>101</b> via a shaft <b>108</b>, and a generator control unit <b>110</b> coupled to the generator <b>106</b>. Where the gas turbine engine <b>101</b> is a multi-spool, the generator <b>106</b> may be coupled to any one of the spools, for example a LP spool such that the generator <b>106</b> may be a LP generator. The generator <b>106</b> generally may be an electrical generator configured to extract energy from the gas turbine engine <b>101</b> and generate electrical power. The electrical power may then be used by one or more application electrical loads <b>118</b> within the vehicle. The application electrical loads <b>118</b> may include, but are not limited to, control systems, actuators, climate control systems, and the like.

The generator control unit <b>110</b> may be configured to control the operation of the generator <b>106</b>, and to communicate with other system components, such as the application electrical loads <b>118</b>. For example, the generator control unit <b>110</b> may command the generator <b>106</b> to distribute electrical power to the application electrical loads <b>118</b> via a power bus <b>116</b>.

The system <b>100</b> may further include a heater <b>112</b> and a heater control unit <b>114</b> coupled to the heater <b>112</b>. The heater <b>112</b> generally may be any electrically operated heating element or circuit configured to receive electrical power to generate thermal energy, including, but not limited to, a heater pad. The heater <b>112</b> generally may have a steady state power limit and a transient power limit. While only one heater <b>112</b> is shown, it should be appreciated that there may be any number of heaters <b>112</b>, where each heater <b>112</b> may be coupled to a separate heater control unit <b>114</b>, or multiple heaters <b>112</b> may be coupled to at least one heater control unit <b>114</b>. The heater <b>112</b> may be located upstream of the compressor <b>102</b> such that it may provide the thermal energy to the inlet air stream <b>120</b>, i.e., heat the inlet air stream <b>120</b>. In one exemplary approach, the heater <b>112</b> may be located in an inlet duct <b>122</b> of the gas turbine engine <b>101</b>. In another exemplary approach in which the gas turbine engine <b>101</b> is a turboprop having a propeller <b>105</b>, the heater <b>112</b> may be located in or around the propeller. It should be appreciated that the heater <b>112</b> may be located anywhere within the gas turbine engine <b>101</b> or the vehicle that thermal energy may be required or desirable, not just upstream of the compressor section <b>102</b>. For example, vehicles often include anti-icing or de-icing systems and/or circuits at various locations where ice buildup is undesirable, such as at the engine inlet, the wings of an aircraft, etc. Such existing systems may be utilized as the heater <b>112</b>, which would eliminate the need to install additional equipment, thereby saving costs to implement the system <b>100</b>. Furthermore, the heater <b>112</b> may be used in lieu of or in addition to batteries, capacitance banks, flywheels, or the like to store excess electrical energy generated by the generator <b>106</b>, as described in more detail hereinafter.

The heater control unit <b>114</b> generally may be configured to control the operation of the heater <b>112</b>. The heater control unit <b>114</b> may be in communication with the generator control unit <b>110</b> and/or the power bus <b>116</b> such that electrical power may be supplied from the generator <b>106</b> to the heater <b>112</b> when required, such as for engine transient conditions. For example, one or more of the application electrical loads <b>118</b> may be suddenly removed, thereby reducing the engine power demand from the gas turbine engine <b>101</b>. However, the gas turbine engine <b>101</b> may not adjust its power output quickly enough to counter the load removal, thereby resulting in excess power, i.e., the engine power is greater than the engine power demand. As such, it may be desirable to transfer the excess power to another load, i.e., the heater <b>112</b>, to prevent the gas turbine engine <b>101</b> from rapidly accelerating. In such situations, the heater control unit <b>114</b> may energize the heater <b>112</b> such that the excess power may be transferred to the inlet air stream <b>120</b> via electrical heat to help maintain engine loading and reduce engine speed increases, thereby helping the engine decelerate. The energy may be reclaimed by the gas turbine engine <b>101</b> for the period during and after the electrical heat is applied. Due to the relatively long time constant (slow response) of the heating system, the reabsorption of heat by the gas turbine engine <b>101</b> may occur after the fuel has been reduced and the gas turbine engine <b>101</b> is decelerating or is at a low power condition.

In another exemplary situation, it may be desirable to increase the engine loading or power demand transiently or to rapidly increase the gas turbine engine <b>101</b> from idle to full power, i.e., within a predetermined time frame. In such a scenario, the gas turbine engine <b>101</b> may be a multi-spool engine having a LP spool and a HP spool, where the generator <b>106</b> is coupled to the LP spool, as mentioned above. When such a power demand is anticipated, the heater control unit <b>114</b> may energize the heater <b>112</b> to increase the electrical power generated by the generator <b>106</b> and generator loading on the LP spool, thereby resulting in an increase in HP speed and fueling. As the power demand increase occurs, the heater control unit <b>114</b> may turn off the heater <b>112</b> in order to reduce the engine power if the power demand exceeds the power available from the gas turbine engine <b>101</b>. The added electrical heat introduced at the engine inlet by the heater <b>112</b> may be at least partially recovered by the gas turbine engine <b>101</b> to assist the HP speed to accelerate. For a dual or triple spool engine, if the engine is being controlled to LP spool speed at low power, then the HP idle speed will increase when the heater <b>112</b> is switched on to provide the benefit of higher engine power and higher HP speed with the onset of the higher power demand.

When it is known when the anticipated engine power demand increase is going to occur, the heater control unit <b>114</b> may energize the heater <b>112</b> at a predetermined time frame, for example five seconds, before the engine power demand actually increases. During this time frame, the heater <b>112</b> may be allowed to exceed its steady state limits transiently. However, if power demand increase is impending but the exact timing is unknown, the heater <b>112</b> may be energized for a longer period of time, where the heater <b>112</b> may not exceed its steady state limit.

There are several benefits to utilizing the heater <b>112</b> in the conditions described above. First, turning the heater <b>112</b> on when there is an anticipated power increase raises the power output of the gas turbine engine <b>101</b> such that when the rapid load increase actually occurs the gas turbine engine <b>101</b> is already outputting more power to absorb it. Second, this may reduce acceleration time (time to output maximum power) of the gas turbine engine <b>101</b>, since the engine HP spool speed is raised from where it would otherwise be if the heater <b>112</b> had been left off and the engine power remained low. Gas turbine engines typically accelerate much faster if the initial power condition is higher. This is because the engine HP spool speed is already elevated, and the compressor surge line usually increases significantly as engine power (HP speed) increases when at relatively low engine power states. Therefore, the engine can take a much larger fuel rate increase and therefore sustain a faster acceleration without problems. Third, the previously generated heat from the inlet may be released during the engine acceleration such that the heat energy is partially re-absorbed into the engine to temporarily boost the inlet energy to assist the acceleration.

Also, when it is anticipated that an increase in power demand will occur, then the engine speed driving the generator <b>106</b> may be raised to the maximum speed limit for low power operation of the generator <b>106</b> and the gas turbine engine <b>101</b>. This may store additional rotational kinetic energy in the system <b>100</b> that may be absorbed as the generator and engine speed droops when the engine power increase occurs.

Installation of the heater <b>112</b> and/or the static structure of the gas turbine engine <b>101</b> at the engine inlet may be designed to have significant heat capacity to allow the release of electrical heat to the inlet air stream <b>120</b> to occur over an extended period of time after the heater <b>112</b> has been switched off, such as when the gas turbine engine <b>101</b> is no longer generating excess power. For example, multiple heaters <b>112</b> may be located at various locations at the engine inlet and staged in operation. Alternatively or in addition, the gas turbine engine <b>101</b> at the inlet, for example the inlet duct <b>122</b>, may be made of a material having a high heat capacity above a predetermined threshold, and/or may be a relatively large structure such that there may be a large available area for heat transfer to the inlet air stream <b>120</b> to occur. This may help reduce the peak temperature of the heater <b>112</b>, increase the specific heat capacity to allow larger amounts of heat to be absorbed, and allow a larger heat flow to the inlet air stream <b>120</b>. In icing conditions, this may allow the heater <b>112</b> to be switched off when the application electrical loads <b>118</b> are applied to reduce the peak electrical power off take. This may also help to minimize the variation in electrical load and therefore loading of the generator <b>106</b> that may occur due to electrical power transients and drop-outs that may occur, as explained above.

The system <b>100</b> may include a system controller <b>124</b> in communication with the gas turbine engine <b>101</b>, the generator control unit <b>110</b>, the heater control unit <b>114</b>, and/or the application electrical loads <b>118</b>. The system controller <b>124</b> may determine when a condition exists, and direct the generator control unit <b>110</b> and/or the heater control unit <b>114</b> to control the operation of the generator <b>106</b> and the heater <b>112</b>, respectively. By way of example only, the condition may be where the engine power demand drops below the engine power, such as when one of the application electrical loads <b>118</b> and/or a mechanical or hydraulic load is removed. Another condition may be when an increase in the engine power demand is anticipated or requested, such as when the gas turbine engine <b>101</b> accelerates from an idle speed within a predetermined time frame.

It should be appreciated that the system of dissipating and storing electrical heat energy and rotational kinetic energy may also be applied to rapidly changing hydraulic or mechanical loads to the system that occur faster than the gas turbine engine <b>101</b> may respond. It should further be appreciated that this system may be applied for cases in which the generator <b>106</b> is driven by a hydraulic motor powered by an engine driven hydraulic pump.

Computing devices, such as the generator control unit <b>110</b> and the heater control unit <b>114</b>, generally include computer-executable instructions such as the instructions of the system controller <b>18</b>, where the instructions may be executable by one or more computing devices such as those listed above. Computer-executable instructions may be compiled or interpreted from computer programs created using a variety of programming languages and/or technologies, including, without limitation, and either alone or in combination, Java™, C, C++, C#, Objective C, Visual Basic, Java Script, Perl, etc. In general, a processor (e.g., a microprocessor) receives instructions, e.g., from a memory, a computer-readable medium, etc., and executes these instructions, thereby performing one or more processes, including one or more of the processes described herein. Such instructions and other data may be stored and transmitted using a variety of computer-readable media.

A computer-readable medium (also referred to as a processor-readable medium) includes any non-transitory (e.g., tangible) medium that participates in providing data (e.g., instructions) that may be read by a computer (e.g., by a processor of a computer). Such a medium may take many forms, including, but not limited to, non-volatile media and volatile media. Non-volatile media may include, for example, optical or magnetic disks and other persistent memory. Volatile media may include, for example, dynamic random access memory (DRAM), which typically constitutes a main memory. Such instructions may be transmitted by one or more transmission media, including coaxial cables, copper wire and fiber optics, including the wires that comprise a system bus coupled to a processor of a computer. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EEPROM, any other memory chip or cartridge, or any other medium from which a computer can read.

Databases, data repositories or other data stores described herein may include various kinds of mechanisms for storing, accessing, and retrieving various kinds of data, including a hierarchical database, a set of files in a file system, an application database in a proprietary format, a relational database management system (RDBMS), etc. Each such data store is generally included within a computing device employing a computer operating system such as one of those mentioned above, and are accessed via a network in any one or more of a variety of manners. A file system may be accessible from a computer operating system, and may include files stored in various formats. An RDBMS generally employs the Structured Query Language (SQL) in addition to a language for creating, storing, editing, and executing stored procedures, such as the PL/SQL language mentioned above.

In some examples, system elements may be implemented as computer-readable instructions (e.g., software) on one or more computing devices (e.g., servers, personal computers, etc.), stored on computer readable media associated therewith (e.g., disks, memories, etc.). A computer program product may comprise such instructions stored on computer readable media for carrying out the functions described herein.

Referring now to <figref idref="DRAWINGS">FIGS. 3A and 3B</figref>, an exemplary method <b>200</b> for managing speeds of the gas turbine engine <b>101</b> during engine transient conditions is shown. Method <b>200</b> begins at block <b>202</b> at which the heater <b>112</b> may be switched off if it is on, and the gas turbine engine <b>101</b> and the generator <b>106</b> may be commanded, for example by the system controller <b>124</b>, to operate at optimum speed for a current power setpoint. At block <b>204</b>, method <b>200</b> may include determining, if an increased engine power demand is anticipated or requested. If no, then block <b>204</b> may proceed to block <b>222</b>. If yes, then method <b>200</b> may proceed to block <b>206</b> at which the speed of the generator <b>106</b> may be increased to a low power generator/engine speed limit. At block <b>208</b>, method <b>200</b> may then include determining if a transient heater limit is exceeded. If no, such as when the heater <b>112</b> is turned off, method <b>200</b> may proceed to block <b>212</b> at which the heater <b>112</b> may be energized to the transient heater power limit. If yes, then method <b>200</b> may proceed to block <b>210</b> at which the heater <b>112</b> may be energized to a steady state power limit. After either block <b>210</b> or <b>212</b>, method <b>200</b> may proceed to block <b>214</b> at which it may be determined whether there has been an actual engine power demand increase. If no, method <b>200</b> may go back to block <b>204</b>. If yes, then method <b>200</b> may proceed to blocks <b>216</b> through <b>220</b> at which the gas turbine engine <b>101</b> may be commanded to rapidly increase in power, the heater <b>112</b> may be switched off, and the engine speed may be allowed to droop to optimal speed for high power operation.

At block <b>222</b>, method <b>200</b> may include determining if the engine power demand is below the engine power, for example if any of the application electrical loads <b>118</b> have been removed. If no, method <b>200</b> may go back to block <b>202</b> to repeat method <b>200</b> until one of the conditions from blocks <b>204</b> and <b>222</b> are present. Alternatively, method <b>200</b> may end. If yes, method <b>200</b> may proceed to block <b>224</b> at which the engine <b>101</b> may be commanded to rapidly decrease in engine power. At block <b>226</b>, method <b>200</b> may then include determining if a transient heater limit is exceeded. If no, such as when the heater <b>112</b> is turned off, method <b>200</b> may proceed to block <b>230</b> at which the heater <b>112</b> may be energized to the transient heater power limit. If yes, then method <b>200</b> may proceed to block <b>228</b> at which the heater <b>112</b> may be energized to a steady state power limit. After either block <b>228</b> or <b>230</b>, method <b>200</b> may proceed to block <b>232</b> at which it may be determined if the engine power is less than the engine power demand or if the engine speed is decreasing and is below an engine speed transient limit. If either one of these conditions is present, method <b>200</b> may proceed to block <b>234</b> at which the heater <b>112</b> may be switched off. If neither one is present, method <b>200</b> may go back to block <b>222</b>. After block <b>234</b>, method <b>200</b> may go back to block <b>202</b> to repeat itself, or alternatively, method <b>200</b> may end.

With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claims.

It will be appreciated that the aforementioned method and devices may be modified to have some components and steps removed, or may have additional components and steps added, all of which are deemed to be within the spirit of the present disclosure. Even though the present disclosure has been described in detail with reference to specific embodiments, it will be appreciated that the various modifications and changes can be made to these embodiments without departing from the scope of the present disclosure as set forth in the claims. The specification and the drawings are to be regarded as an illustrative thought instead of merely restrictive thought.

All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those knowledgeable in the technologies described herein unless an explicit indication to the contrary in made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.